How Do I Work With Images On Chocolate Icing?

I need a clever way to carefully remove choc icing from a cake, & replace with white icing just under where the images will be placed. Do I spread entire cake with choc bc, then carefully scoop out areas to fill in with white bc where the images will go? In all my years of doing graduation cakes, this is the first request I've had for a white cake with chocolate icing AND edible images. I don't even know how well this will work, but would love to hear from all of you who have accomplished this. Thank you so much!